Shock wave lithotripsy (SWL) of kidney stones is not always successful. Stones in a significant percentage of patients fail to fragment completely. These patients may undergo more than one SWL session with no positive outcome, and then must be treated by an invasive procedure (e.g., percutaneous nephrostomy or ureteroscopy). Even when SWL is successful, the physician has no good guidelines to follow in determining how many SW's to administer, and patients may receive many more SW's than is required to break up the stone. If stone fragility could be predicted during diagnosis, the physician could select the best treatment, including the optimal number of SW's for SWL, or in the case of SW-resistant stones move to an alternative therapy. Helical computed tomography (CT) has the potential to help predict stone fragility. However, we lack sufficient knowledge about the structure of kidney stones to know the CT features that distinguish easy-to-break stones from those that are SW-resistant and should not be treated by SWL. Hypothesis: Urinary stones that are susceptible to lithotripter SW's can be distinguished radiologically from those stones that are SW-resistant. Plan: The proposed research will characterize fragility-relevant structures that are visible within kidney stones by mu CT. We will identify features (including mineral compositions and internal structures) that correlate with--and thus, can be used to predict-the susceptibility (or resistance) of stones to lithotripter shock waves, working through the following Specific Aims: 1. Calibrate micro computerized tomography (mu CT) imaging of urinary stones so that stones can be analyzed for composition and for three-dimensional structure using this non-destructive analytical tool. 2. Determine the degree to which similar stone analysis can be accomplished using present helical CT technology. 3. Determine if stone fragility in SWL correlates with CT-visible structure. 4. Determine if fragility in SWL for some stones might be determined by features below the resolution of CT. The long-term goal of this work is to enable the physician to predict the fragility of kidney stones at diagnosis so that the best treatment option can be chosen.